In general, an automatic transmission includes a friction device, such as a clutch or a brake, which is connected with an input shaft, a planetary gear set, or each operation element of the planetary gear set in the case of the transmission. In this configuration, it needs to align the center axis of the friction device and the center axis of the input shaft with the center axis of the transmission case to secure the exact positions.
For example, according to an automatic transmission in the related art, as shown in FIG. 1 showing the configuration of main parts, an input shaft 3, a friction device 5, and a center support 7, etc. are disposed in a transmission case 1, in which input shaft 3 and friction device 5 are assembled such that the center axis are aligned with the center axis X of transmission case 1, and the assembly process is as follows.
Transmission case 1 has a large-diameter portion that is formed in a relatively large diameter at a side and connected with a torque converter and a small-diameter portion that is formed in a relatively small diameter at the other side opposite to the large-diameter portion and forms the rear end of the automatic transmission. Accordingly, a worker stands transmission case 1 such that the large-diameter portion is positioned upward while the small-diameter portion faces the floor and then sequentially assembles various parts including input shaft 3 inside the case.
However, when positioning center support 7 equipped with a piston in a pressure chamber to provide a fastening force to friction device 5 into transmission case 1 in the assembly direction (indicated by an arrow), the worker cannot see with naked eyes interference between piston 9 and a plate spring 11 that provides a return force to friction device 5, such that it is difficult to assemble friction device 5, thereby reducing the work efficiency. This is because, as shown in FIG. 2, plate spring 11 has elastic pieces 11a that protrude with inclination at regular intervals on the inner circumference and plate spring 11 should be assembled such that elastic pieces 11a are alternately positioned with pressing ends 9a that protrude at regular intervals on the front end of piston 9.
In detail, after plate spring 11 is positioned in transmission case 1, when piston 9 is assembled with center support 7 and then center support 7 is positioned in transmission case 1 in the assembly direction, the portion where pressing ends 9a of piston 9 and elastic pieces 11a of plate spring alternately connected is covered by center support 7. Therefore, the worker should fit the alternate connecting portion between pressing ends 9a and elastic pieces 11a while circumferentially rotating center support 7.
A snap ring is disposed on the inner circumference of transmission case 1 to firmly support a side of plate spring 11.
According, a new-typed elastic member without the alternate connecting structure of pressing ends 9a of piston 9 and elastic pieces 11a of plate spring 11 has been proposed, which is shown in FIG. 3.
That is, a snap ring 13 is disposed on the inner circumference of transmission case 1 in the assembly direction (indicated by an arrow), a side of a wave coil spring 15 is supported by snap ring 13 as shown in FIG. 3, and pressing ends 9a of piston 9 disposed in pressure chamber 7a of center support 7 is disposed through the insides of snap ring 13 and wave coil spring 15, which is a new type.
According to this structure, because there is no direct connecting portion between piston 9 and wave coil spring 15, it does not need to circumferential rotate center support 7 for assembly. However, unless the center axis of wave coil spring 15 placed on snap ring 13 is exactly aligned with center axis X of transmission case 1, assembly defect is generated by contact between pressing ends 9a of piston 9 and the inner circumference of wave coil spring 15. Accordingly, when it is wrong assembly, a portion of wave coil spring 15 is deformed by pressing ends 9a of piston and normal function may not be achieved.
Reference numeral ‘5a’ that is shown in FIGS. 1 and 3 indicates a plurality of plates that is spline-connected with the inner circumference of transmission case 1, ‘5b’ indicates discs that are alternately interposed between the plates, and ‘5c’ indicates a hub that is spline-connected with the outer circumference of discs 5b. 
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.